Copy UV Islands to another UV set?
Maybe UVMagic addon already in Blender. You can copy from objects to other objects, faces etc. its simple to use, hope it helps!
Features

11:40 Copy/Paste UV (Among faces in UV/Image Editor)
0:07 Copy/Paste
UV (Among objects)
0:51 Copy/Paste UV (Among faces in 3D View)
1:51 Transfer UV

Tutorial and feature list here

https://www.youtube.com/watch?v=BKZX3Xac7X4